The "having more mental space" argument is very interesting to me. There's some interesting science around this across a number of disciplines. The most readable intro is probably this one but the idea goes deep: if the organism has to devote cycles to survival, there are less cycles to devote to longer-term projects. This shakes out everywhere, including mating strategies.
So I think it's plausible, at least. But I'm trying to guard against telling myself a story that I want to hear.
Taking your point a bit off topic, I sometimes wonder about this factor when I see those unlikely animal friends or guy with a pet grizzly bear videos. It seems like even apex predators, when they're reliably well-fed, can be quite friendly to animals they would just kill out in nature.
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Yes. When organisms have enough, pro-sociality can get expansive. I think about this all the time. It's an interesting lens to invert: if someone is being a giant douche, what else is probably true, or has been true?
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I try to keep that in mind, too (it's not always easy). We don't know what other people are going through and it's good to grant them some benefit of the doubt, until they prove they don't deserve it.
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